Three-dimensional coordinate measuring machine

ABSTRACT

A three-dimensional coordinate measuring machine includes a base, a moving mechanism provided on the base, and a probe moved by the moving mechanism, the three-dimensional coordinate measuring machine measures coordinates of a surface position of an object to be measured by using the probe, the moving mechanism includes: a linear guide using a mechanical bearing; and an air bearing mechanism provided in parallel to the linear guide, one of ends of the moving part is attached to a linear moving unit that moves by the linear guide and the other is attached to the air moving part so that the other end can swing with respect to the air moving part, and the air bearing mechanism absorbs a difference in the height change between the linear guide and the air bearing mechanism by the air bearing.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/324,764, filed Jul. 7, 2014. The entire contents of which are herebyincorporated herein by reference.

BACKGROUND

1. Technical Field of the Invention

The present invention relates to a three-dimensional coordinatemeasuring machine, and particularly, to a moving mechanism of athree-dimensional coordinate measuring machine.

2. Related Art

A three-dimensional coordinate measuring machine is used to measurecoordinates of an outline of an object. In the three-dimensionalcoordinate measuring machine, moving mechanisms that move in three-axisdirections, i.e., an X-axis, a Y-axis, and a Z-axis orthogonal to oneanother, are sequentially configured on a base and a displacementmeasuring instrument is provided in a member (third moving part) capableof moving in the three-axis directions in the final stage, and then thecoordinates of the surface position of an object are calculated bycombining the displacement when a probe of the displacement measuringinstrument is caused to come into contact with the outline of the objectand the coordinate values in the three-axis directions at that time. Thecoordinates of the position to which each moving mechanism has movedserve as the base of the coordinates to be measured, and therefore, thecoordinates of movement are required to be highly accurate.

The moving mechanism of the three-dimensional coordinate measuringmachine etc. is implemented by using a linear guide.

FIG. 1A and FIG. 1B are diagrams illustrating a linear guide: FIG. 1A isa perspective view illustrating an external appearance and FIG. 1B is asection view.

The linear guide has a rail 1 and a moving unit 2 that slides and moveson the rail 1. As illustrated in FIG. 1B, the moving unit 2 is incontact with the rail 1 via bearing balls 3 and at the time of movement,the bearing ball 3 rotates. As illustrated in FIG. 1A, there existrotation components P, Y, and R in three directions in which the movingunit 2 rotates with respect to the rail 1. P is called pitching, Y,yawing, and R, rolling.

When configuring a moving mechanism, in order to remove the influence ofthe above-described rotations, a plurality of linear guides is used. Forexample, two moving units that move on the same rail are attached to thesame moving part. Due to this, it is possible to reduce the influence ofthe pitching P and the yawing Y. In this case, the rail is only one, andtherefore, it is comparatively easy to perform attachment.

Further, there is a case where a plurality of rails and a plurality ofmoving units are used. For example, two rails are arranged in paralleland two moving units that move on each rail are attached to the samemoving part. In this case, as described above, two moving units may beattached to each rail. In such a case, four moving units are used. Dueto this, it is possible to reduce the influence of rolling R, inaddition to that of the pitching P and the yawing Y.

FIG. 2 is a diagram illustrating a configuration example of a movingmechanism of a three-dimensional coordinate measuring machine. Thisconfiguration is a cantilever system.

The three-dimensional coordinate measuring machine has a base 11 formedof a stone surface plate of compound artificial marble etc., a Y column21 provided on one of sides of the base 11, two Y-axis rails 22A and 22Bprovided in parallel on the Y column 21, a Y moving part 31 that moveson the Y-axis rails 22A and 22B, two X-axis rails 32A and 32B providedin parallel on the Y moving part 31, an X moving part 40 that moves onthe X-axis rails 32A and 32B, a Z column 41 fixed to the X moving part40 and which extends in the vertical direction, two Z-axis rails 42A and42B provided in parallel on the Z column 41, and a Z moving part 50 thatmoves on the Z-axis rails 42A and 42B. To the Z moving part 50, adisplacement measuring instrument 51 is attached and a measuring probeof the displacement measuring instrument 51 is caused to come intocontact with the surface of an object to be measured. In the cantileversystem moving mechanism, it is possible to access the top of the base 11from any direction except from the backside, and therefore, there is anadvantage that arrangement of an object to be measured, check of thecontact position of the measuring probe, etc., can be performed easily.

Since two moving units are arranged on each rail, groups of four movingunits are attached to the Y moving part 31, the X moving part 40, andthe Z moving part 50. In the configuration in FIG. 2, the two railsprovided in parallel are arranged in proximity to each other on the samesurface of the same member, and therefore, it is possible to easilyarrange them with a high degree of parallelization.

However, in the cantilever system moving mechanism in FIG. 2, althoughthe Y moving part 31 is supported by the two rails 22A and 22B and thefour moving units, the portion close to the end is supported, andtherefore, displacement occurs on the other end due to bending. Theamount of bending changes in moment as the X moving part 40 moves. Inother words, the rigidity of the Y moving part 31 is insufficient.

In order to reduce the influence of bending (rigidity) of theabove-described cantilever system moving mechanism, a configuration inwhich both ends of the Y moving part 31 are supported may be used.

FIG. 3 is a diagram illustrating another configuration example of themoving mechanism of the three-dimensional coordinate measuring machine.In FIG. 3, only the configuration for moving the Y moving part 31 isillustrated and the moving mechanisms of the other axes are not shown.The moving mechanism of the type in FIG. 3 is referred to as an L type.

The L-type moving mechanism of the three-dimensional coordinatemeasuring machine in FIG. 3 has the same configuration as that in FIG. 2in that one of end parts of the Y moving part 31 is supported by the twoY-axis rails 22A and 22B provided in parallel on the Y column 21, butdifferent from the configuration in FIG. 2 in that a support member 60for supporting the end part on the opposite side of the Y moving part 31is provided and the undersurface of the support member 60 is supportedby a sub guide 61 arranged on the base 11. The sub guide 61 is, forexample, a linear guide.

In the configuration in FIG. 3, the straightness of the sub guide 61 isrequired to be kept at a very high degree of accuracy. It is possible torepresent an error of the straightness of the sub guide 61 as, forexample, a variation in the height of the surface of the base 11. If theheight 1 of the surface of the base 11 in the sub guide 61 changes byΔ1, the height of the end part on the opposite side of the Y moving part31 also changes, but one end of the Y moving part 31 is supported by twolinear guides of the Y column 21, and therefore, this is equivalent tobeing fixed. Because of this, the Y moving part 31 bends (warps) and theheight of the end part on the opposite side changes by Δ2, resulting inequilibrium. If such bending occurs in the Y moving part 31, the Zmoving part 50 inclines and the position of the measuring probe of thedisplacement measuring instrument 51 changes by Δ3, and therefore, anerror in coordinate measurement occurs.

The bending of the Y moving part 31 changes accompanying the movement inthe Y-axis direction and also changes depending on temperature etc. Itis possible to correct to a certain degree the error in the contactposition of the measuring probe due to bending of the Y moving part 31by a correction formula calculated based on the measurement results of areference object, but there is such a problem that it is difficult toaccurately correct the influence by the change in the amount of bending.

FIG. 4 is a diagram illustrating a configuration example of the movingmechanism of the three-dimensional coordinate measuring machine. Thisconfiguration is a so-called bridge system.

In the bridge system three-dimensional coordinate measuring machine, twoY columns 21A and 21B are provided on the sides in opposition to eachother on the base 11 and one Y-axis rail 22A is provided on the Y column21A and one Y-axis rail 22B on the Y column 21B, respectively. In thecase where two moving units are used on each rail, to the Y moving part31, four moving units that move on the two rails 22A and 22B areattached. Other portions are the same as those in the case of FIG. 2.

In the bridge system three-dimensional coordinate measuring machine inFIG. 4, it is necessary to mount the rails after machining the railattachment surfaces of the two Y columns 21A and 21B to which one set ofrails is attached so that the degree of parallelization and straightnessare of very high accuracy, and therefore, there is such a problem thatthe manufacturing costs will be very high. Further, in the bridge systemthree-dimensional coordinate measuring machine in FIG. 4, the accessonto the base 11 is limited, and therefore, there is such a problem thatit becomes difficult to arrange an object to be measured, to check thecontact position of the measuring probe, etc.

There is also known a so-called gate type three-dimensional coordinatemeasuring machine in which the Y moving part 31 is formed into the shapelike a gate and the Y-axis rails 22A and 22B are provided on the base,but the same problem as that described above exists because it isnecessary to machine the bottom surface of the gate type Y moving part31 so that the degree of parallelization and straightness are of veryhigh accuracy.

RELATED DOCUMENTS

[Patent Document 1] US20110313706A

[Patent Document 2] JP2012-042267A

SUMMARY

As explained above, the cantilever system moving mechanism has such aproblem that rigidity is insufficient and the bridge system movingmechanism and the L-type moving mechanism resembling the former havesuch a problem that the manufacturing cost will be increased becausevery high machining accuracy is required.

In order to solve the above-described problems, in the three-dimensionalcoordinate measuring machine of the present invention, one of end partsof a moving part is supported by a linear guide and the other end partis supported by an air moving part that moves along an air bearing slideguide part provided in parallel to the linear guide.

The three-dimensional coordinate measuring machine of the presentinvention includes: a base; a moving mechanism provided on the base; anda probe moved by the moving mechanism. The three-dimensional coordinatemeasuring machine measures coordinates of a surface position of anobject to be measured by using the probe. The moving mechanism includes:a linear guide using a mechanical bearing; and an air bearing mechanismprovided in parallel to the linear guide.

In the three-dimensional coordinate measuring machine of the presentinvention, in the case where the degree of parallelization andstraightness of the linear guide and the air bearing slide guide partare insufficient and the relative height of the linear guide and the airbearing slide guide part changes depending on the position of movement,it is possible to absorb to a certain extent a difference in the heightchange by the air bearing. If the height of the other end part of themoving part changes, the inclination of the moving part changes, i.e.,rolling occurs, but the moving part is supported by the linear guide,and therefore, it is possible to absorb this by the rolling Rillustrated in FIG. 1A. Due to this, the inclination of the moving part,i.e., the rolling changes, but bending does not occur in the movingpart. If there is no bending, the change due to an error hasreproducibility, and therefore, it is possible to make highly accuratecorrection by applying the current correction technique and it ispossible to control the position of movement with high accuracy. Inother words, in the present invention, the rolling R, which hasconventionally been suppressed as small as possible, is permittedpositively and one of ends of the moving part is supported by the linearguide and the other is supported by the air bearing, and the change inthe relative height of the portions supporting the moving part isabsorbed by the air bearing, and then the change in the inclination ofthe moving part is absorbed by the rolling permitted for the linearguide and the link part in which an other end of the moving part canswing with respect to the air moving part.

Further, by the combined use of the linear guide, which is a mechanicalbearing, and the air bearing, it is possible to reduce a reciprocatinghysteresis by setting the friction surface only in the line of themechanical bearing slide surface and installing a drive point, on whicha drive power for moving the moving part is applied, on the frictionsurface.

The moving part may have the L-type configuration having a columnillustrated in FIG. 3, the bridge type configuration having two columnsillustrated in FIG. 4, or the gate type configuration with no columnprovided.

In the L-type configuration having a column, a column provided on one ofsides of the base and having a mount surface parallel to the basesurface is provided, a linear guide of the first axis moving mechanismis provided on the mount surface of the column, and the air moving partis attached to the support member provided on the other end part of themoving part and supported by the air bearing slide guide part providedon the base.

The moving part needs to be attached so that the moving part can swingwith respect to the air moving part and this link part is configured soas to have, for example, a tip end part in the shape of a sphere and areceiving part for receiving the tip end part in the shape of a sphere,at least part of which is a conical surface.

According to the present invention, it is possible to implement a highlyaccurate three-dimensional coordinate measuring machine with a simpleconfiguration and at a low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are diagrams illustrating a linear guide: FIG. 1A isa perspective view illustrating an external appearance and FIG. 1B is asection view;

FIG. 2 is a diagram illustrating a configuration example of a movingmechanism of a three-dimensional coordinate measuring machine;

FIG. 3 is a diagram illustrating another configuration example of themoving mechanism of the three-dimensional coordinate measuring machine;

FIG. 4 is a diagram illustrating a configuration example of the movingmechanism of the three-dimensional coordinate measuring machine;

FIG. 5A and FIG. 5B are diagrams each illustrating a basic configurationof the three-dimensional coordinate measuring machine of the presentinvention;

FIG. 6A and FIG. 6B are diagrams illustrating a configuration of athree-dimensional coordinate measuring machine of an embodiment in whichthe present invention is applied to the L type; and

FIG. 7 is a diagram illustrating a configuration example of the linkmechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5A and FIG. 5B are diagrams each illustrating a basic configurationof the three-dimensional coordinate measuring machine of the presentinvention. FIG. 5A illustrates the case of application to the L typehaving a column and FIG. 5B illustrates the case of application to thegate type. In FIG. 5A and FIG. 5B, only the configuration for moving theY moving part is illustrated and the moving mechanisms of the other axesare not illustrated.

As illustrated in FIG. 5A, the L-type three-dimensional coordinatemeasuring machine to which the present invention is applied has the base11, the Y column 21, the Y (first) moving part 31 that moves on the topsurface of the Y column 21, and the support member 60 that supports theY moving part 31. The Y column 21 is provided along one of sides of thebase 11 and the top surface of the Y column 21 is parallel to thesurface of the base 11. The Y moving part 31 is connected to the rail ofone linear guide provided on the top surface of the Y column 21 via aliner moving unit and moves by the one linear guide. In FIG. 5A, theconnection part of the Y moving part 31 and the one linear guide isdenoted by reference numeral 70. The Y moving part 31 is furtherprovided with the X-axis moving mechanism and the Z-axis movingmechanism and the coordinates of the position of the probe of thedisplacement measuring instrument 51 attached to the Z moving part 50moves in the three-axis directions.

The other end part of the Y moving part 31 is supported by the supportmember 60. The lower part of the support member 60 is supported by theair moving part so that the other end can swing with respect to the airmoving part. The air moving part and the air bearing slide guide partprovided on the base 11 in parallel to the linear guide on the topsurface of the Y column 21 configure an air bearing mechanism 80. Due topresence of the air bearing mechanism 80, even in the case where therelative height of the linear guide and the air bearing slide guide partchanges, it is possible to absorb to a certain extent a difference inheight change by the air bearing mechanism. Further, the lower part ofthe support member 60 is supported by the air moving part so that theother end of the Y moving part 31 can swing with respect to the airmoving part and at the same time, even if the inclination of the Ymoving part 31 changes, there is only one linear guide, and therefore, acertain magnitude of rolling can be absorbed. Due to this, even ifrolling occurs in the Y moving part 31, bending does not occur in the Ymoving part 31 and it is possible to control the position of movementwith high accuracy by correction. Further, by the combined use of thelinear guide, which is a mechanical bearing, and the air bearing, thefriction surface can be set only in one line of the slide surface of themechanical bearing, and therefore, it is possible to reduce areciprocating hysteresis by installing the drive point on the frictionsurface.

In the L-type system moving mechanism illustrated in FIG. 5A, the linearguide is lifted up higher than the surface of the base 11, andtherefore, it is possible to reduce the distance between the position ofthe center of gravity of the Y moving part 31 and the drive point(linear guide) compared to that in the gate type moving mechanism, to beexplained next, and it is further possible to reduce the weight of the Ymoving part 31. Due to this, it is possible to reduce pitching of the Ymoving part 31 at the time of acceleration/deceleration and to reducethe drive force necessary to improve movement responsiveness or toimplement the same movement responsiveness. Further, it is possible toeasily access the top of the base 11 from any direction except for thebackside, and therefore, it is possible to easily arrange an object tobe measured and to check the contact position of the measuring probe.

A illustrated in FIG. 5B, the gate type three-dimensional coordinatemeasuring machine to which the present invention is applied differs fromthe case of the L type in FIG. 5A in that the Y column 21 is notprovided and the configuration is formed into a gate type in which the Ymoving part 31 is configured by the parallel portion 61, a first supportmember 62, and a second support member 63.

The lower part of the first support member 62 is supported by theconnection part 70 with one linear guide provided along one of sides ofthe base 11. The lower part of the second support member 63 is supportedby the air bearing mechanism 80 like the support member 60 in FIG. 5A.

In the gate type moving mechanism illustrated in FIG. 5B, both thelinear guide 70 and the air bearing slide guide part of the air bearingmechanism 80 are provided on the top surface of the base 11, andtherefore, it is easy to keep at high accuracy the degree ofparallelization of the linear guide 70 and the air bearing slide guidepart. On the other hand, there is such a problem that the gate type Ymoving part 31 is heavy in weight compared to that of the L typeillustrated in FIG. 5A and is easily affected by a pitch error.

In FIG. 5A and FIG. 5B, the examples of the L type and the gate type areexplained, but it is also possible to similarly apply the presentinvention to other systems, such as the bridge type.

FIG. 6A and FIG. 6B are diagrams illustrating a configuration of athree-dimensional coordinate measuring machine of an embodiment in whichthe present invention is applied to the L type. FIG. 6A is a front viewand FIG. 6B is a side view. In FIG. 6A and FIG. 6B, parts other than theY moving part are the same as those of the conventional examples, andtherefore, only the configuration for moving the Y moving part isillustrated and the moving mechanisms of the other axes are notillustrated.

The three-dimensional coordinate measuring machine of the embodiment hasthe base 11 formed by a stone surface plate of compound artificialmarble etc., the hollow Y column 21 provided on one of sides of the base11, one Y-axis rail 22 provided in parallel on the Y column 21, two Ymoving units 23A and 23B that move on the Y-axis rail 22, the Y movingpart 31 attached to the Y moving units 23A and 23B, two X-axis railsprovided in parallel on the Y moving part 31, and four, in total, Xmoving units 33AA, 33AB, 33BA, and 33BB that move on the two X-axisrails. On these units, an X moving part etc. is configured, but it isnot illustrated or explained.

To the end part of the Y moving part 31 on the opposite side of the sidesupported by the Y column 21, the cylindrical support member 60 isattached. The lower part of the support member 60 is supported by an airmoving part 82 by means of a link mechanism 81 so that the end part ofthe Y moving part 31 can swing with respect to the air moving part 82.Along the side on the base 11 in opposition to the air moving part 82,an air bearing slide guide part 83 is provided. The air bearing slideguide part 83 is, for example, a groove having the width of the airmoving part 82 extending in the Y-axis direction. The air moving part 82jets out air supplied from the outside to the surface of the air bearingslide guide part 83 and is capable of moving in the Y-axis direction inthe floating state at a fixed height. In other words, the air movingpart 82 is capable of moving in the Y-axis direction, but does notchange its position in the X-axis direction and is capable of changingits position by a finite amount in the Z-axis direction. Here, theportion configured by the air moving part 82 and the air bearing slideguide part 83 is referred to as the air bearing mechanism 80.

FIG. 7 is a diagram illustrating a configuration example of the linkmechanism 81. As illustrated in FIG. 7, the air moving part 82 isarranged in opposition to the surface of the air bearing slide guidepart 83 on the top surface of the base 11. The air moving part 82 has areceiving part 92 having a hole at least part of which is in the shapeof a cone. At the tip end of the support member 60, a hemispherical tipend part 91 is provided and comes into contact with the hole in theshape of a cone of the receiving part 92. Here, the tip end part 91 ispressed against the cone-shaped hole of the receiving part 92 by theweights of the first moving part 31, the X- and Z-axis mechanismsconfigured thereon, the support member 60, etc. Due to this, the supportmember 60 (Y moving part 31) is supported by the air moving part 82 sothat the Y moving part 31 can swing with respect to the air moving part82.

Desirably, the relative height of the top surface of the Y column 21,i.e., the rail 22 of the one linear guide, and the surface of the airbearing slide guide part 83 is fixed, but some errors produced inmanufacture are inevitable. In the embodiment, even in the case wherethe relative height of the rail 22 of the linear guide and the airbearing slide guide part 83 changes, it is possible to absorb to acertain extent a difference in height change by the air bearingmechanism 80. Further, the lower part of the support member 60 issupported by the air moving part so that the Y moving part 31 can swingwith respect to the air moving part 82 and even if the inclination ofthe Y moving part 31 changes, there is only one linear guide, andtherefore, it is possible to absorb a certain magnitude of rolling. Dueto this, even if rolling occurs in the Y moving part 31, no bendingoccurs in the Y moving part 31 and only the Y moving part 31 inclines,and the amount of inclination has reproducibility, and therefore, it ispossible to control the position of movement with high accuracy bycorrection.

Although the embodiments of the present invention are explained, theembodiments described above are merely for explaining the invention andit is possible for a person skilled in the art to easily understand thatthere can be various kinds of modified examples in the scope of claims.

What is claimed is:
 1. A three-dimensional coordinate measuring machinecomprising: a base; a moving mechanism provided on the base; a probemoved by the moving mechanism, wherein the three-dimensional coordinatemeasuring machine measures coordinates of a surface position of anobject arranged on the base by using the probe; a linear guide mechanismprovided on one side of the moving mechanism and having a mechanicalbearing, which is arranged higher than the base; and an air bearingmechanism provided on another side of the moving mechanism at a heightsimilar to a height of a surface of the base and lower than a height ofthe linear guide mechanism.
 2. The three-dimensional coordinatemeasuring machine according to claim 1, further comprising a drive unitfor moving the moving mechanism provided on the linear guide, whereinthe drive unit is not provided on the air bearing mechanism.